1. Field of the Invention
The present invention relates to an improved motorcycle power transmission and brake assembly, and more particularly to an improved motorcycle power transmission and brake assembly wherein a rear wheel of the motorcycle is driven and braked through an intermediary idle sprocket assembly.
2. Brief Description of the Prior Art
Conventional and most frequently utilized motorcycle drive or power transmission assemblies incorporate a drive sprocket, a rear wheel sprocket and an endless chain which interconnects the drive and rear wheel sprockets of the motorcycle. The drive sprocket is driven, usually through an intermediate transmission and clutch assembly, by the engine. The axle of the rear wheel of the motorcycle is mounted to a fork shaped elongated member, which is usually referred to as a swing arm. The swing arm is mounted to the frame of the motorcycle through a swing arm pivot axle so that the rear wheel axle is able to move on an arc relative to the frame. The swing arm is usually also connected to the frame through a pair of springs, shock absorbers or the like.
In traditional motorcycle construction either a brake drum or a brake disk is incorporated in, or a fixedly attached to the hub of the rear wheel. In the event a brake disk is used, a mechanically or hydraulically actuated caliper type device is caused to frictionally engage both sides of the disk whenever a braking action is desired.
As is well known in the motorcycle manufacturing and designing arts, mounting the rear wheel of a motorcycle on a pivotable swing arm is necessary in order to enable the rear wheel to move up and down as irregularities or bumps of the road surface are traversed by the motorcycle.
As is further well known in the motorcycle manufacturing arts, an inherent disadvantage of the above summarized motorcycle drive and brake system is that as the rear wheel axle moves up and down on an arc carried by the swing arm, a distance between the rear wheel sprocket and the drive sprocket changes. Therefore, the endless chain must be designed, and adjusted in tension to reasonably accommodate the above noted variations in the distance between the drive sprocket and the rear wheel sprocket. This can, however, be accomplished only with a limited degree of success. Consequently, as all motorcycle drivers know, broken chains, too tight chains, too loose chains, and the requirement for periodically readjusting the tension of the chains represent problems which continuously require attention by the motorcycle repairing industry.
An additional disadvantage of the conventional motorcycle drive and brake system construction is caused by the weight of the brake drum or brake disk which is incorporated in, or is fixedly attached to the hub of the rear wheel. As is well known by those skilled in the art, in order to improve the handling characteristics of a motorcycle, it is desirable to minimize unsprung weight. Yet the weight of the rear wheel brake drum or brake disk is undesirable, unsprung weight.
Still another disadvantage of conventional motorcycle drive and brake system construction is that during braking, the weight of the motorcycle (including the weight of its rider) tends to shift forward thereby decreasing the traction of the rear wheel on the road surface. Therefore, rear wheels of motorcycles have a marked tendency to "skid" during hard braking. Expressed in other words, in conventional motorcycles the forward shifting of the weight during braking occurs at the "least opportune" moment, precisely when increased traction of the rear wheel on the road surface would be desirable for effective braking and directional control of the motorcycle.
In order to overcome the first noted disadvantage of conventional motorcycle construction, namely the requirement for frequent adjustment of the drive chain of the motorcycle, the prior art has provided certain types of alternative power transmission constructions and add-on devices. These by-and-large eliminate, or more or less alleviate, the chain problems continuously troubling conventional motorcycles. U.S. Pat. No. 3,548,963, for example, describes a two-wheeled vehicle in the nature of a small portable motorcycle, wherein a pulley and an idler sprocket are mounted to rotate in unison about the swing arm pivot axle. The pulley is connected by a belt with a drive shaft of the engine and the idler sprocket is connected by a chain with the rear sprocket of the rear wheel. Similar constructions utilizing a double row idler sprocket are described in U.S. Pat. Nos. 3,974,892; 3,252,537; 2,468,367; 1,143,793, and in British Pat. No. 260,474 and French Pat. No. 2,307,695. An advantage of utilizing a double row or similar idle sprocket rotating about the swing arm pivot axle, as is described in the above-noted U.S. patents, is that the slack or tension of the drive chain is unaffected by the irregular up-and-down movement of the rear wheel axle.
U.S. Pat. No. 2,468,367 describes, in addition to the above noted double row sprocket or like idle sprocket assemblies, a brake drum which is mounted on the same axle with the double row sprocket assembly.
U.S. Pat. No. 4,034,821 describes a motorcycle drive system wherein a pair of idler sprockets are mounted to the frame, "pinching" the drive chain. These idle sprockets more or less automatically adjust the slack of the drive chain.
Additional disclosures relating to motorcycle chains and drive systems or the like are found in U.S. Pat. Nos. 4,039,200; 1,780,705; 3,722,612; 4,061,050, and 4,077,485.
The present invention represents a significant improvement over the above-noted prior art in that, in accordance with the present invention, slack or temporary overtightening of the chain and resulting chain failure is eliminated, the unsprung weight of the rear wheel of the motorcycle and of associated braking system is minimized, and traction of the rear wheel of the motorcycle is increased during braking.